The River Quaggy Flood Alleviation Scheme
The flood alleviation scheme for the Quaggy is the key to restoring this river. Turned one way it would have locked the door against this river ever coming back to life; turned the other way it opens the door to a full restoration of the river.
When the National Rivers Authority (NRA) – now the Environment Agency – first proposed a new flood alleviation scheme in 1990 they planned to use the technique of channelising the river. The Friends of the Quaggy – now QWAG – were able to show that a large part of the River Quaggy’s flooding problem was due to previous channelising, which was rushing massive amounts of water into Lewisham. The Friends of the Quaggy suggested that, rather than further channelising the river, the NRA should break the Quaggy out of its concrete channel and restore the river and its flood plain in Sutcliffe Park, at the same time creating an attractive feature along with nature study areas and picnic places.
The NRA tested this idea and found that it would work – and would be significantly cheaper than their original scheme. Furthermore, the idea of an attractive river in a relandscaped park with new education facilities and places to take the family proved very popular with local people. A survey for Greenwich Council showed 78% of local people in favour of the proposed changes to the park.
It took five years of campaigning by QWAG, eight years of planning and re-design by the Environment Agency and much argument with Greenwich Council over planning permission. But in June 2003 the work to restore the river and its flood plain in Sutcliffe Park finally started. The door is now open to making the River Quaggy the first fully restored urban river in the world.
. These photos were taken on 3rd July 2004, just after the restoration work in Sutcliffe Park was completed.
Sutcliffe Park – how it works
Today the River Quaggy flows across the surface of Sutcliffe Park. But the old underground concrete culvert survives along the eastern and northern borders as a vital component of the flood alleviation scheme.
The Quaggy enters the park at the south-eastern corner from under Eltham Road. Near to the granite weir (the ‘low-flow inlet’), a sluice controls the distribution of the water – either down the weir into the park or along the underground culvert. At the park’s far north-western corner, a ‘low-flow outlet structure’ re-routes the river back into the culvert.
Flow is regulated to ensure a healthy river. In dry conditions the greater proportion (around 50 litres per second), is directed into the park as a low-flow channel. As the volume of water increases, more diverts into the culvert. In flood conditions, two cubic metres a second could flow down the river while 18 cubic metres a second enters the culvert.
Crucial to the scheme is a constriction (a ‘flume’) built into the culvert along its northern limb. Only a limited amount of water can pass. Flood water will back up to a level where it begins to flow out into the park through grids of a specially constructed zone known as the ‘high-flow inlet’.
The park will slowly fill from its northern end, taking 12 hours to reach its capacity of 85,000 cubic metres. At a foot below the level of the perimeter footpath, excess water will be safely directed back into the culvert through another set of grids (the ‘spillway’) immediately downstream of the flume. After a flood, the water could take 12 hours to drain away through the ‘low-flow outlet’.
The flow of water is largely controlled by careful shaping of the park itself, avoiding the need for mechanical controls altogether.